Electrical apparatus



June 20, 1961 J. M. GRAHAM ETAL 2,989,660

ELECTRICAL APPARATUS Filed Sept. 29, 1953 Ticyl- INVENTORS James M.GRAHAM LOUIS H. SEGFILL QTTORNE 5 Unite v.

Delaware Filed Sept. 29, 1953, Ser. No. 382,902

6 Claims.

This invention relates to electrical apparatus and more particularly todevices adapted for use in creating sparks or arcs, such as may beuseful in ignition systems for combustion engines and the like.

One of the objects of the present invention is to provide a novellyconstructed sparking device of the type adapted for use as a spark plugor igniter plug in an engine ignition system.

Another object of the invention is to provide novel apparatus of thetype embodying a shunted surface spark gap which is particularly adaptedfor use in a condenser discharge circuit for producing high energypulses or sparks at relatively low voltage.

A further object is to provide a novel method of fabricating a sparkingdevice of the type which may have a relatively narrow annular spark gap.

Still another object is to provide a novel spark gap assembly whichmakes possible the use of desirable electrode materials, the use ofwhich has not been practical in comparable devices heretofore known.

The invention makes practical the use of smaller quantities of highlyadvantageous but expensive electrode materials.

A still further object is to provide a spark or igniter plug for use inan ignition system for combustion engines which is novelly constructedto insure a uniform annular spark gap and one which will withstand longand rugged use without danger of failures in operation.

Another object is to provide a sparking device of the above characterwhich is so constructed as to substan tially eliminate any possibilityof the leakage of gases therethrough.v

Another object is to provide a novel sparking device which is verycompact and which presents only a small area tothehot gases ofcombustion in an engine cylinder.

Another object is to provide a novelly constructed sparking device whichhas a high pre-ignition rating and which is substantially non-fouling.

The above and further objects and novel features of the presentinvention will more fully appear from the following detail descriptionwhen the same is read in connection with the accompanying drawings. Itis to be expressly understood, however, that the drawings are for the.purposes of illustration only and are not intended as a definition ofthe limits of the invention.

In the drawings, wherein like reference characters refer to likepartsthroughout the several views,

. FIG..1 is a longitudinal sectional view of one form of igniter plugembodying the present invention;

FIG. 2 is a bottom view of the device shown in FIG. 1;

FIG. 3 is an exploded view showing parts of the device of FIG. 1 priortofinal assembly, some of said parts being in unfinished form forassembly purposes.

.The single embodiment of the invention illustrated in the drawings, byway of example, is in the form of a spark plug or igniter plug for usein the ignition system of a combustion engine, but it will be understoodthat the use of the invention is not so limited. The type of deviceillustrated may be used for ignition purposes in any combustion chamber,such as in the cylinders of a piston engine or in thecombustion chambersof jet and gas turbine type engines. Parts or all of the novelconstruction illustrated may also be used in other. environments as aspark gap, such as for controlling the flow of electrical States Patentenergy in an electrical circuit, and particularly for controlling thedischarge of electrical condensers.

In the form shown in the drawings, the igniter plug comprises a tubularmetallic shell 10 which has external threads 11 by means of which theplug may be operably mounted in the wall of a combustion chamber, or thelike. Other suitable known mounting means may, of course, be employed.An internal flange 12 at the lower end of shell 10 supports a novelspark gap assembly S which will be hereinafter more fully described.Extending upwardly from assembly S along the central axis of the shellis a spindle 14 which provides an input terminal 15 that may beconnected to a source of electrical energy, such as a charged electricalcondenser. The annular space within the shell above assembly S andaround spindle 14 is filled with an insulating mass 16 and a sleeve 17of ceramic or other suitable insulating material. The mass 16 may beformed by a glassy substance or the like having a high meltingtemperature, such as lead borosilicate glass, and serves as a seal andas a mechanical binder for the assembled parts. One suitable compositionfor the mass 16 comprises equal parts of lead oxide and Pyrex glass. Alead cobalt silicate glass frit may also be used. The mass 16 isrendered plastic by heat during assembly and compressed to a highdensity. Thin layers of mass 16 enter the small annular spaces betweensleeve 17 and shell 10 and between said sleeve and spindle 14. Theeffects of differences in the coefficients of expansion of the parts arethus minimized. The upper end of shell 10 is internally threaded at 18for receiving a gland nut or shielding barrel 19 which engages the outerend surface of sleeve or bushing 17 and complements the mass 16, ifnecessary, for holding the parts in assembled relation.

The novel spark gap assembly S comprehended by this invention comprises,in the form shown, an outer shell 20, the central portion of which has aclose fit in shell 10 and rests upon flange 1'2. Preferably, shell 20has a reduced portion at the outer or lower end thereof which has aforce fit within said flange and terminates flush with the end of shell10. The upper or inner end of assembly shell 20 is also reduced toprovidea thin wall section and an annular space 21 into which theinsulating mass 16 extends. Shell 20 is provided at itsouter end with aninternal flange 22 that serves as a seat or support for an annular discor ring electrode 23. The latter is preferably made of a substance, suchas tungsten, which will resist erosion or deterioration by electricalsparking, high heat and the products of combustion within the combustionchamber. The electrode may be and prefer: ably is soldered into shell 20by means of silver solder, or its equivalent. The lower face of flange22 may be tapered as shown, but this is not essential.

Centrally disposed within shell 20 is a center electrode support 24having an enlarged head 25, which terminates flush with the outer endsof shells 10 and 20. The periphery of head portion 25 is preferablytapered oppositely to the taper of flange 22 to provide a taperedannular groove. Seated on the upper or inner surface of head portion 25and closely surrounding the spindle of support 24 is a second annulardisc or ring electrode 26 which may be soldered to the support 24, 25and may be of tungsten or other suitable electrode material. Theadjacent diameters, i.e., the inner and outer peripheries of discs orrings 23 and 26, respectively, are such that an annular spark gap 27 isprovided therebetween. Said gap may be made quite wide or the same maybe very small. In one practical embodiment, a gap as small as about .005inch has been found desirable.

, Secured between shell 20 and electrode support 24 for accuratelymaintaining the same in concentric spaced relation is a ring 28 of rigidinsulating material, such as aluminum oxide. This ring has a close fitaround the spindle of support 24 and within shell 20. The lower face 29of said ring is ground flat to provide good surface engagement.withelcctrode rings 23 and 26 andis treated with silver nitrate or itsequivalent or is impregnated in any suitable manner with a metallic orother electrically conductive substance to render said surface highlyresistive or semi-conductive to electrical current. Thus, although avoltage impressed across electrodes 23 and 26 may be too low to jump gap27, it may nevertheless create a flow of energy through or along thesemiconductive surface of ring 28 and thereby sufliciently ionize thegaseous medium in the gap to permit the low voltage to bridge the gapand create a spark or arc. When the energy is supplied by a chargedcondenser or its equivalent, the spark thus created may embody asubstantial amount of energy even though the voltage is relatively low.

The gap assembly S is made into a rigid unit by spinning the edges ofthe thin walls of shell 20 and of the counterbored inner end of support24 inwardly and outwardly, respectively, onto ring 28. Brass or othersuitable washers 30 and 31 are preferably provided between theinsulating spacer ring and the turned over portions of members 20 and24. The upper surface of ring 28 is preferably stepped, as shown, toprovide a safe creepage path or flash-over distance between the upperends of shell 20 and support 24. The inner or upper portion of theassembly S is surrounded by and virtually embedded in mass 16. Thus, thelatter not only serves as a seal to prevent the flow of gases from thecombustion chamber, but also serves as means for mechanicallypositioning and securing the spark gap assembly S within shell 10.

For assembly purposes, shells 10.and 20 are initially made withextensions or skirts 33 and 34, respectively, and central electrodesupport 24 is provided with an extension 35. A ring 37 is located aroundextension 35 within skirt 34 and, if desired, ring 37 may be in the formof a flange formed integrally with extension 35. These extensions andring 37 are carefully machined to accurately fit within one another sothat when the parts are assembled, accurate concentricity thereof, andhence uniformity in the width of gap 27 will be assured. Thisconcentricity is of greatest importance when the width of gap 27 issmall. The electrode rings 23 and 26 are first soldered to shell 20, 34and support 24, 35 with a high melting point solder, such as silversolder. The shell and support are then assembled with spacer ring 28,washers 30 and 31, and centering ring 37. With the parts of theelectrode assembly thus held in assembled relation, the upper edges ofshell 20 and support 24 are spun into firm engagement with Washers 30and 31. The electrode assembly is then placed in shell 10, the skirt 34having a drive fit within extension 33. Spindle 14 is then inserted withthe lower reduced end thereof threaded into the counter-bore in support24. The spindle may have a force fit in support 24, or a solder ring maybe interposed between a downwardly facing shoulder on the spindle andthe upper end of support 24 to insure a good electrical connection andserve as an anchor for the spindle. The bore of shell is then filled toa point below a shoulder 36 with powdered glass or other suitablefusible insulating material having a high melting point and bushing 17is seated on top of the powdered mass. Heat is then applied, such as byelectrical induction or by gas flames applied to the outer surface ofshell 10, to fuse the powdered mass within shell 10. While said mass isin a plastic or molten state, pressure is applied to press bushing 17against said mass and firmly compress the latter into all availablespace between bushing 17 and the electrode assembly S, and into andaround said bushing. The application of pressure is continued while theparts are permitted to cool. After the parts have cooled, the extensions33, 34 and 35 76 are machined off, leaving the structure as illustratedin full lines in FIG. 1. Nut 19 may then be screwed into place againstbushing 17 to complement the mass 16.

There is thus provided by the present invention a novel spark gap devicewhich may be fabricated in accordance with a novel method to insureaccurate concentricity of electrodes to provide a small, uniform annularspark gap. The novel construction provided also insures against gasleakage therethrough which would reduce the operating efficiency andlife thereof. Additionally, the structure comprehended is of a sturdyconstruction which will withstand physical shock and vibration as wellas wide and rapid changes in temperature. The materials used are suchthat erosion by electrical sparking is reduced to a minimum, therebyprolonging the useful life of the device. The small number of partsemployed are all of simple construction which may be inexpensivelymanufactured and readily assembled.

Although only a single embodiment of the invention has been illustratedin the accompanying drawings and described in detail in the foregoingspecification, it isto be expressly understood that the invention is notlimited thereto. For example, materials other than those specificallymentioned as being suitable may be used. Platinum, alloys of platinumand other materials known to be well adapted for making electrodes maybe used inlieuof tungsten and the silver deposited on the lower face ofinsulator 28 may be replaced by other materials such as carbon, graphiteand the like. Various other changes, such as in the specific design andarrangement of the parts illustrated may also be made without departingfrom the spirit and scope of the invention as the same will now beunderstood by those skilled in the art.

What is claimed is:

1. In an electrical sparking device, a tubular shell having an internalflange at one end thereof, a spark gap assembly comprising a tubularshell member having a sliding fit in said shell and a pilot extensionhaving a tight fit in said flange, said member being seated on saidflange, center electrode means in said member and in spark gap relationtherewith and an insulating sleeve interposed between said member andsaid center electrode means, a conductor extending through said shellfrom said center electrode means, and a mass of insulating material setfrom a plastic state under pressure within the shell and completelyfilling the annular space in said shell immediately above said assemblyand around said conductor.

2. A spark gap device comprising a tubular shell having an internalflange at one end thereof, a spark gap assembly seated on said flangeand comprising a tubular shell member having an internal flange at oneend thereof, an annular electrode seatedon said flange, a centerelectrode support extending through said member, said support having anenlarged head portion and a spindle, an annular center electrode seatedon said head portion within and in spark gap relation to saidfirst-named annular electrode, and an insulating sleeve seated on saidannular electrodes and surrounding said spindle within said memher, theother end of said member having an internal flange engaging a shoulderon said sleeve and the upper end of said spindle having an externalflange engaging the end of said sleeve, whereby the parts are held inassembled relation, a pilot extension of said member having a force fitin said shell flange, and a mass of insulating material set from aplastic state under pressure within the shell and filling the space insaid shell immediately above said assembly around an extension of saidcenter electrode support, said mass having intimate contact with saidshell for holding the shell and assembly in assembled relation.

3. A spark gap device as defined in claim 2 wherein said mass is a glasshaving a high melting point, such as lead borosilicate glass.

4. The method of fabricating a spark gap assembly which includes thesteps of making a tubular shell member having an internal shoulder and acylindrical pilot extension, centrally supporting a center electrodesupport with a pilot extension in a pilot in said cylindrical pilotextension, locating concentric electrode rings in the same plane on saidshoulder and on a shoulder on said center electrode support, insertingan insulating sleeve in said shell member on said electrode rings andaround said center electrode support, turning the end of said memberinwardly over said sleeve and turning the end of said center electrodesupport outwardly over said sleeve.

5. The method of fabricating a spark gap device which includesfabricating a spark gap assembly as defined in claim 4, inserting saidassembly into a tubular shell having a tubular pilot extension in whichthe pilot extension on said shell member has a force fit, securing saidassembly in said shell, and thereafter machining off said pilotextensions.

6. The method of fabricating a spark gap device as defined in claim 5wherein the step of securing said assembly in said shell includes thesteps of placing a fusible insulating material in the shell above theassembly, fusing said material by application of heat, and applyingpressure to said fused material while the latter cools tosolidification.

References Cited in the file of this patent UNITED STATES PATENTS1,009,867 Terry Nov. 28, 1911 1,272,954 Horning July 11, 1918 1,999,785Rohde Apr. 30, 1935 2,408,642 Hopps et al. Oct. 1, 1946 2,497,862 ChuyFeb. 21, 1950 2,501,826 McCarthy Mar. 28, 1950 2,572,209 Smits Oct. 23,1951 2,615,441 Bychinsky Oct. 28, 1952 2,625,922 Smits Jan. 20, 19532,684,665 Tognola July 27, 1954 2,747,123 Tognola May 22, :19562,861,014 Sheheen Nov. 18, 1958 2,874,322 Bychinsky Feb. 17, 1959FOREIGN PATENTS 631,386 Great Britain Nov. 2, 1949 868,459 France Oct.6, 1941

